1. Field of the Invention
The invention generally concerns a scissors-type lifting platform for motor vehicles and more particularly relates to a relatively simple, quiet, wear resistant lifting platform.
2. Background Discussion
In their xe2x80x9cdownxe2x80x9d position, scissors-type lifting platforms should be as low as possible in order to facilitate the positioning of the load to be lifted. In particular, lifting platforms for motor vehicles should, when in their xe2x80x9cdown position,xe2x80x9d project as little as possible above the floor in order to facilitate the driving on of the vehicles. In the case of typical scissors-type lifting platforms there also, however, arises the problem that the scissors spars, which are able to swivel against one another, in the starting phase of the lifting movement an unfavorable lever geometry can be created for the lifting device.
To solve this problem, known scissors-type lifting platforms used a so-called expansion lever which expands over the scissors-type lifting platform rod assembly in the starting phase of the lifting movement.
German Utility Model 92 05 900 describes a scissors-type lifting platform with an expansion lever of this type. In the case of this lifting platform, the expansion lever, which is swivellably supported on one scissors spar is, however, supported on a counterplate which is arranged on the other scissors spar. Through the sliding movement of the expansion lever on the counterplate, high mechanical stresses ensue, in particular in the case of a heavy load, which can lead to increased wear on the sliding surfaces. Replacement of the elements which slide over one another is costly and associated with correspondingly high costs of material and maintenance.
It is accordingly a primary purpose of the invention to provide a scissors-type lifting platform with a wear-resistant and easily maintained expansion mechanism. This purpose is accomplished according to the invention by means of the support device containing at least one rotatably lodged cylinder body for supporting the expansion lever.
In the scissors-type lifting platform according to the invention, during the swivelling process of the scissors spar, the expansion lever rolls away from the lowest position on one or more rotatably supported rolling bodies, which substantially reduces friction. It is therefore possible to avoid the use of costly high-grade materials or the use of exchangeable sliding plates. It is moreover possible to avoid noises created in conventional expansion mechanisms by sliding friction between the expansion lever and the counterplate, particularly in dry running. By means of the roll-away movement of the expansion lever over the rolling bodies according to the invention, it is possible to avoid extensive wear and a disturbing noise.
In a particularly advantageous embodiment, the support device has, for example, two support cylinders lying next to one another to act as rolling bodies. The support surface of the expansion lever is made in the form of steps so that, for example, the expansion lever, which is actuated by a pressure medium cylinder can, during the process of the rise of the lifting platform, first be supported on the first support cylinder and then on the second one. The lever action of the expansion lever during the process of expansion is thereby optimized.
According to another useful embodiment of the invention, the scissors spars can have two scissors arms parallel to one another, which can be connected by cross-supports or the like. The scissors spars can, however, also be of a different design.
In a particularly stable embodiment, the support cylinders can be rotatably supported via bearing bushings in two parallel bearing supports on one of the scissors spars.
In the configuration of scissors spars with parallel scissors arms, the bearing supports can, for example, be arranged on a connecting plate between the two scissors arms.